Enable placement-api in devstack job config
Enable placement-api in devstack job config

It is now a requirement for n-cpu per:
http://lists.openstack.org/pipermail/openstack-dev/2017-January/111295.html

Split OVERRIDE_ENABLED_SERVICES for readability

Change-Id: I96d0e6e6b4b3363b99f66a304f394221c7c75dbd

openstack/networking-sfc,openstack/networking-sfc